AN ESSENTIAL piece of kitchen equipment is a pair of heavy-duty, high-quality shears.

A pair of shears is actually two knives joined together at a central point by a screw. The knives swivel about the central point and the leverage created makes cutting easier: a good theory, but not always effective in practice. More often than not, Kitchen shears are poorly mnaufactured and no joy to use.

When selecting a pair of kitchen shears begin with the same criteria used for choosing a knife. The tool should be made of a material that will not stain, pit or rust as a result of its contact with moist and acidic foods. The substance should be hard enough so that it will not break under pressure but be soft enough so the edges can be resharpened. The handles must be comfortable to grip and present a surface that can be held by wet hands. The overall design should allow for easy cleaning when food particles lodge within the structure.

Quite logically, many of the companies that produce excellent knives also produce excellent shears. The J. A. Henckels Twin works in Soligen, Germany, fabricate all-purpose kitchen shears made of top-quality, nonstaining; high carbon steel. There is a serrated edge on the blades that makes it easy to cut pieces of raw meat, fish or poultry. The handles have been given an industrial plastic coating that gives a good holding surface for wet and slippery hands. Between the pivot screw and the end of the handle are two oval openings. The one with serrates edges is designed for cracking nuts and removiing screwtop bottle tops. The other will pry off caps.The end of each handle has a flat tab that acts as a screwdriver or can be used for more top prying.

Because the screwdriver tabs are located at the base of each handle, they are to the side of the tool's central axis. This results in a poor leverage system which works well only with the lightest of jobs. Remember this is a kitchen shears and not a carpenter's screwdriver and you will not be disappointed in its functioning. The tool is eight inches long and retails for about $27.50.

Though the Henckels' shears described above do not have a tension spring, many kitchen shears come equipped with a strong spring between the handle, which pushes the handles apart and requires a serious effort to close. This effort is passed along in the form of cutting power. When selecting a kitchen shears with a tension spring, bear in mind that these springs present a welcome environment for food particles. If the spring device is going to be difficult to clean, avoid that model. You must also make sure that any kitchen shears with a tension spring come equipped with a strong, safe and dependable latch on the handle to hold the tool closed.

When selecting a shears for cutting poultry, you will be confronted with two styles and two theories.Some cooks feel straight blades are better, easier to control and more effectively sharpened and curved. The other group believes that only a curved blade will get down into various anatomical areas of a big bird. The extremists within the curved blade society feel that a highly curved blade with an extreme arc will break down and do difficult jobs without bringing your hand into contact with the hot food.

An exceptional example of this latter design is the good-looking chromed home steel shears with black plastic-coated handles distributed by Norbert Stryer and retailing for about $20.They are only 10 1/4 inches long and are joined by a visible spring of twisted wire that is far easier to clean than the more common exposed springs of flattened, coiled steel. One blade has a serratted edge to help cut through skin and meat, and it is arched in one area to cut through bones. The bone cutting arch is an essential element in good poultry shears.

Recently, I have been using a kitchen shears called SNIPS. The blades are made in West Germany of a steel alloy and set into plastic handles. There is an easily cleaned spring device and a storing sheath that joins a mount that can attach to any flat surface by means of a strip of epoxy tape. It was first demonstrated to me by its manufacturers' agent who proceeded to cut a nickel in half, thereby illustrating the true value of the tool -- and the nickel. Since than I have used it with considerable success on everything from poultry bones to kite string. SNIPS retails for about $9.49.